Upper Precambrian General Stratigraphic Scale of Russia: Main problems and proposals for improvement

Research subject. Main problems of the General Stratigraphic Scale (GSS) of the Upper Precambrian including uncertainties in the hierarchy of subdivisions are analyzed.Results. Prospects for detailing the Upper Precambrian GSS are discussed, along with questions of its correlation with International Chronostratigraphic Chart (ICSC) and establishing the lower boundaries of chronostratigraphic subdivisions. The importance of unifying the existing views is emphasized.Conclusions. It is proposed to carry out the following reforms of GSS: to abolish Acrothemes / Acrons; to approve the Proterozoic (as well as the Archean) as an Eonotheme / Eon; to minimize the use of terms “Upper Proterozoic” and “Lower Proterozoic”; to assign the Riphean and Vendian to the rank of Erathem / Era (while preserving the status of the Vendian as a System / Period); to consider Burzyanian, Yurmatinian, Karatavian and Arshinian as Systems / Periods of the Riphean. Attention is focused on the Upper Riphean-Vendian interval. The lower boundary of the Upper Riphean (Karatavian) was proposed to establish according to the first appearance of the Trachyhystrichosphaera sp. microfossils. Then, the Terminal Riphean (Arshinian) lower boundary should be traced to the base of the tillites formed during the global Sturtian glaciation (which approximately corresponds to the base of the Cryogenian in ICSC). Apparently, the Vendian lower boundary may be raised to the level of the top of the Gaskiers tillites, as the deposits of the last major glaciation in the Precambrian. The indicated proposals are substantiated. It is necessary to form work groups to develop solutions.

Gold deposits ot the Guiana shield

The article provides a comparative analysis of Guyana and Venezuela major deposits within the Quartzstone ore field (Guyana). From the northwest to the southeast (from Venezuela to Brazil), more than 10 ore gold deposits are currently known, their total resources (including previous production) exceed 2,600 tons of gold (excluding the Amapari and Salamangoni deposits in Brazil). Almost all of Guyana deposits are confined to the Lower Proterozoic greenstone belts of the Guiana shield identified and explored for the past 15–20 years. The geological features of the largest deposits (Omay, Aurora, Toroparu, Tassawini and Monosi) are presented in the article.

Composition and age of monacite fragments from superior jurassic terrigenous sediments of bazhenov formation foundation (multan area in west siberia)

Bazhenov Formation is regarded as the main oil-bearing stratum mothering nearly all the fields of the Western Siberia Oil-Gas-bearing Megabasin. Presently, it is one of the most studied formations of Siberia and, probably, Eurasia as a whole. While there is an enormous amount of studies devoted to the Bazhenov Formation, there are no detailed mineralogical studies at the modern hardware level. The age and sources of the terrigenous materials of the formation have not been studied as well. We have explored the detrital monazite from the upper-Jurassic terrigenous sediments of the Multan Area at the foundation of the Bazhenov Formation in the central part of Western Siberia, Surgut District. All the detrital rare earth phosphate is of the cerium kind being a monazite-(Се). The mineral is rather dissimilar in respect of its chemical properties, especially, the content of thorium. Some fragments have been subjected to superposed secondary changes. The detrital monazite is rounded to various degrees which is indicative of the various distances from the rare earth phosphate orebody washout. As per the chemical data, most of the monazite has been washed out from the medium and basic rocks (probably subalkaline or alkaline) as well as the sialic rocks (granitoids and associated veins). According to the chemical dating, most of the monazite fragments have been washed out of the very ancient Proterozoic formations and lower-Proterozoic rocks. Terrigenous materials derives probably from the rock assemblages of the eastern and south-eastern fringes of the Western Siberian megabasin such as the Proterozoic Yenisei Ridge or Lower-Proterozoic blocks of the Altay and Sayan Faulting.

Application of remote sensing for detection of zones of cataclastic and metasomatic rocks on the area of the Uvatsky ore cluster (Eastern Sayan)

Interpretation materials of the Russian space survey «Resource-P» (Geotone) in the visible and infrared bands made it possible to identify crush belts and faults of the northeastern, sublatitudinal and submeridional strike that determine the structural position of uranium mineralization within the Uvat ore cluster in the East Sayan. The principal possibility of using a high-resolution multi-zone space survey (3 m) for detecting metasomatically altered ore-bearing rocks of the Lower Proterozoic and Riphean-Paleozoic carbonate-terrigenous deposits was determined.

Study of mineralogical variability of ferruginous quartzites of productive strata of the eastern wing of the Petrovsky synclinal fold with using diagram Mm-Mo

Relevance of the problem. Petrovsky deposit is promising area for the extraction of magnetite ores. Detailed research on this deposit was carried out in the 80 years of the last century, but with the deepening and expansion of the pit data from previous studies have lost their relevance. In 2016-2018 years, in the north-eastern part of the deposit, an in-mine exploration in the direction of the eastern wing of the Petrovsky synclinal fold was carried out.Analysis of previous research. Petrovsky deposit of ferruginous quartzites is located in the remote southwestern part of the area of the Right Bank magnetic anomalies. Two groups of rocks were defined in the geological structure of the deposit: the crystalline rocks of the Precambrian base and the loose Cenozoic deposits that were on the top of them. Rocks of the Precambrian Age are highly metamorphosed and dislocated ones of the crystalline base and are represented by Archean and Lower Proterozoic formations. Lower Proterozoic formations are represented by the Ingul-Ingulets series which is divided by the (bottom up): zelenorichenska, artemivska, radionivska suites. The Artemivska suite is productive in the territory under investigation.In the structural plan, the Petrovskiy deposit is a compressed synclinal fold, the western wing of which is taper out, and the eastern wing extends in the northern direction. In connection with this, the object of research was the eastern wing.Purpose and tasks of research. The main purpose of the study was identification of the mineralogical variability of ferruginous quartzites, the allocation of mineralogical varieties of ores according to their chemical composition and to determine the regularities of expanding of these varieties within the productive strata of the eastern wing. These tasks were resolved using chemical analysis of rocks data, calculation of magnetic module MM and oxidation module MO, and the construction of a diagram in the coordinates of magnetization-oxidation of iron (MM-MO).Presentation of the main material of the article. Within the eastern wing of the Petrovsky synclinal fold, the eight mineralogical varieties of the ore were identified: silicate quartzites with magnetite, silicate-magnetite quartzites, magnetite-silicate quartzites, magnetite quartzites with hematite, hematite-magnetite quartzites, magnetite-hematite quartzites, hematite quartzites with magnetite. In the boundaries of the work area of a regular change of varieties of ores from hematite quartzites with magnetite in the central parts to silicate quartzites with magnetite on the periphery was established. In the same direction the regularities of changing the content of Fetot., Femagn. and sulfur (S) were elaborated. However, the authigenic-mineralogical zonality of the productive strata of the eastern wing of the syncline structure of the deposit was disturbed as a result of the overprint of metasomatic processes caused by the formation of bodies of aegirine and rebekitic metasomatites on the basis of ferruginous quartzites was established.